COVID-19 IMAGING

 COVID-19 is a viral disease also known as SARS-CoV-2 or severe acute respiratory syndrome coronavirus 2.
The diagnosis is made by a positive PCR test, which is highly specific.
CT(Computed Tomography) has a higher sensitivity but lower specificity and can play a role in the diagnosis and treatment of the disease.

👉Clinical Features    

COVID-19 usually presents with fever (85%), cough (70%) and shortness of breath (43%), but abdominal and other symptoms are possible and the disease can be asymptomatic.

Overall mortality rate is 2.3% in some series of patients who had a positive test for COVID-19.
Since we do not know the number of people who were infected but not tested for the virus, the actual mortality rate of all the people that are infected is probably much lower.

Illness severity can vary from mild to critical.

• Mild: no symptoms, mild coughing and fever.
• Severe: dyspnea, hypoxia or > 50% lung involvement on imaging.
• Critical: respiratory failure, shock, multi-organ failure.

👉PCR-test

The PCR-test is very specific, but has a lower sensitivity of 65-95%, which means that the test can be negative even when the patient is infected.
Another problem is, that you have to wait for the test results, which can take more than 24 hours, while CT results are available right away.
Common laboratory findings in COVID-19 are a decreased lymphocyte count and an increased CRP and high-sensitivity C-reactive protein level.

👉Chest CT

Ground glass:

Ground glass (GGO) pattern is the most common finding in COVID-19 infections.
They are usually multifocal, bilateral and peripheral, but in the early phase of the disease the GGO may present as a unifocal lesion, most commonly located in the inferior lobe of the right lung.

Crazy paving:

Sometimes there are thickened interlobular and intralobular lines in combination with a ground glass pattern. This is called crazy paving.

It is believed that this pattern is seen in a somewhat later stage.

Vascular dilatation: A typical finding in the area of ground glass is widening of the vessels (arrow).

Traction Bronchiectasis: Another common finding in the areas of ground glass is traction bronchiectasis (arrows).

Subpleural bands and Architectural distortion: In some case there is architectural distortion with the formation of subpleural bands.

CT involvement score:

The severity of the lung involvement on the CT correlates with the severity of the disease.

Visual assessment:
The severity on CT can be estimated by visual assessment.
This is the easiest way to score the severity.
The CT images show a 25% involvement by visual assessment.

Severity score:
Another method is by scoring the percentages of each of the five lobes that is involved:

1. < 5% involvement
   
2. 5%-25% involvement
   
3. 26%-49% involvement
   
4. 50%-75% involvement 
   
5. > 75% involvement. 
   

The total CT score is the sum of the individual lobar scores and can range from 0 (no involvement) to 25 (maximum involvement), when all the five lobes show more than 75% involvement.

👉Possible Role Of CT

CT can play a role in:

• Triage of patients:
  - no COVID-19
  - possible or most likely COVID-19
  - severity of the disease
• Prediction of worsening
• Prediction of improvement
• Problem solver